1. Field of the Invention
The present invention relates to a shaft with grooves for generating a dynamic pressure in a dynamic pressure fluid bearing adapted for use in a light deflecting device of a laser beam printer or the like. Also, the present invention relates to a motor with a dynamic pressure fluid bearing employing said shaft, adapted for use in a light deflecting device of a laser beam printer or the like.
2. Related Background Art
In such a light deflecting device, there has been employed a dynamic pressure fluid bearing for realizing non-contact rotation of the shaft in order to achieve a high precision in the device.
The shaft of such a dynamic pressure fluid bearing is provided with fine grooves for generating a dynamic pressure, and the working precision of said grooves is an important factor, governing the rotational reliability of the dynamic pressure fluid bearing. For forming said grooves, there have been proposed following methods.
A first method is to form the grooves for generating the dynamic pressure, by etching areas on curved surface of the shaft, not covered by a resist. FIG. 13 is a schematic cross-sectional view of a dynamic pressure generating groove formed by such etching, and an undercut 32a is formed on the internal wall, close to the aperture of a dynamic pressure generating groove 32, formed on the curved surface of the shaft 31.
A second method utilizes a rolling. As shown in FIG. 14, a dynamic pressure generating groove 42 formed by the rolling on a shaft 41 often shows a shoulder 42a at the aperture of said groove.
A third method is to form a film of a material capable of easily absorbing a laser beam on curved surface of a shaft member, and to form grooves for dynamic pressure generation by eliminating said film with a laser beam, as disclosed in the Japanese Patent Laid-Open Application No. 62-1886.
The prior art explained above has been associated with the following drawbacks.
Because of the undercut in the etching method and the shoulder in the rolling method, the grooves for dynamic pressure generation show complex cross-sectional shape, and fluctuate in the cross-sectional area along the longitudinal direction. For this reason, the dynamic pressure generated during rotation fluctuates, leading to an uneven revolution or vibration of the shaft. Also, the method utilizing the laser beam involves a high cost because of the complexity of the apparatus.